Polymers are known exhibiting liquid crystalline behavior either in solution or in the melt which contribute to desirable properties when formed into either highly ordered fibers or other fabricated structures. The most commonly used class are the aromatic polyamides, typified by poly(p-benzamide), which exhibit liquid crystalline behavior in certain solutions or dopes, and are thus known as lyotropic polymers. An exemplary disclosure of such polymers is U.S. Pat. No. 3,671,542 to Kwolek (June 20, 1972). These polymers are relatively easy to form, but are difficult to handle and must be cast into derived forms (fibers and films) from solution.
Certain aromatic polyesters are known which are liquid crystalline in the melt and are thus thermotropic. U.S. Pat. Nos. 4,140,846 to Jackson, Jr. et al. (Feb. 20, 1979), 3,890,256 to McFarlane et al. (June 17, 1975), 3,991,013 to Pletcher (Nov. 9, 1976), 4,066,620 to Kleinschuster et al (Jan. 3, 1978), 4,075,262 to Schaefgen (Feb. 21, 1978), 4,118,372 to Schaefgen (Oct. 3, 1978); 4,156,070 to Jackson, Jr. et al (May 22, 1979) and 4,159,365 to Payet (June 26, 1979) are representative of such thermotropic polyesters. Known polymers of this class must be formed by melt polymerization, and these polymers have not found wide use. These polyesters exhibit little, if any, solubility in most solvents.
One such thermotropic polyester is phenylhydroquinone terephthalate, as described in U.S. Pat. No. 4,159,365 to Payet. While this material has good low temperature properties, the phenylhydroquinone monomer is difficult to prepare and expensive. Furthermore, all of the known thermotropic polyesters lose their good properties at their glass transition temperature which also does not generally exceed 100.degree. C.
Poly(ester carbonates) are a known class of polymers useful in a variety of articles where high performance is desirable. Such polymers are not, however, generally formed into fibers and are not known to exhibit the properties of the aromatic polyamides or other liquid crystalline material of either the lyotropic or thermotropic type. Such poly(ester carbonates) conventionally include as the principle dihydric aromatic alcohol a bisphenol such as bisphenol-A which would be regarded in a nomenclature of B. P. Griffin et al., British Polymer J. 147 (1980) as a non-linear monomer and include carbonate moieties which are highly flexible. Thermotropic poly(ester carbonates) are described in European Published Patent Application No. 0015856 (Sept. 17, 1980) to Rhone- Poulenc Industries containing methylhydroquinone as the preferred diol (optionally replaced up to 30% by hydroquinone) and various proportions of terephthalate and carbonate. While the monomers forming the terephthalate and carbonate moieties are readily available, methylhydroquinone (or its alternates, the chloro, bromo or ethyl compounds) are generally quite expensive. Furthermore, these poly(ester carbonates) have low glass transition temperatures and thus lose good mechanical properties on heating to 100.degree. C.